A contractile vacuole (CV) is a subcellular structure (organelle) involved in osmoregulation. It occurs mainly in amoebae and in unicellular algae. Previously, it was known as pulsating or pulsed vacuole. Chlamydomonas is an established model system of green algae (16,–18). The cells contain two CVs located at the front end of the cell near the basal bodies (19). The ultrastructure of chlamydomonas CV has been studied in detail (3, 19, 20). At the end of the diastole, the CV has a spherical shape about 2 μm in diameter. During systole, the CV collapses and fragments into smaller vesicles/vacuoles ranging in size (100 to 200 nm). These vacuoles then merge with each other to form a new large spherical CV at the end of the diastole. As in other systems, proton pumps have been implicated in CV function in chlamydomonas (20). We recently isolated CHlamydomona CV mutants by insertion mutagenesis and showed that the exocyst component SEC6 is necessary for CV function (3).
However, not much is known about the basic physiology of CV/osmoregulation function in chlamydomonas. Here we describe the basic regulation of CV activity in chlamydomonas and their adaptation to environments of different osmotic forces. We also discuss the role of aquaporins in osmoregulation in chlamydomonas. Weiss (1983a) described the less coated vesicles associated with the less mating structure that appear to originate from the vacuol contractile region, and Denning and Fulton (1989b) characterized the purified clathrin-coated vesicles by fractionation of the sucrose gradient. Denning and Fulton (1989a) suggested that these vesicles may be involved in the recycling of the vacuol membrane. Domozych and Nimmons (1992) used G. kupfferi to study the absorption of cationic ferritin in the endomembrane system and concluded that contractile vacuole may also work in endocytosis. The number of CVs per cell varies depending on the type.
Amoebae have one; Dictyostelium discoideum, Paramecium aurelia and Chlamydomonas reinhardtii have two; and huge amoebas, like Chaos carolinensis, have a lot of them. In some single-celled eukaryotic organisms (e.B amoebae), cellular waste such as ammonia and excess water is excreted by exocytosis because the contractile vacuoles fuse with the cell membrane and emit waste into the environment. In parametric, which probably has the most complex and sophisticated CV, the vacuole is surrounded by several channels that absorb water from the cytoplasm by osmosis. Once the channels have filled with water, it is pumped into the vacuole. When the vacuole is full, it expels water through a pore of the cytoplasm that can be opened and closed. Protozoa have transient foods or digestive vacuoles. The number of these membrane-bound cellular organelles depends on the body`s eating habits. Some species may have a lot of them, while others may contain only one or two at a time. In ciliates, food vacuoles are formed at the base of the. A mutant of C.
moewusii without contractile vacuoles was described by Guillard (1960). This strain survives in high osmotic pressure media (0.1 million concentrations of a variety of sugars and salts are sufficient), but lyses in 0.1 M of glycerol, urea, ethanol or ethylene glycol. Denning and Fulton (1989a) showed that the cells of this mutant form small anterior vesicles that fuse into larger vacuoles, but these do not interact with the plasma membrane and do not complete systolic discharge. Treatment of wild-type cells with the calcium chelator EGTA to block membrane fusion resulted in a similar accumulation of vacuoles that did not complete the systoles. Contractile vacuoles are considered to be stores of acidic calcium (Patel and Docampo, 2010), and it has been suggested that they are involved in the secretion and signaling of ca2+. In D. discoideum, the expression of CVC Ca2 +-ATPase PAT1 is upregulated as a function of calcineurin when cells are grown in a calcium-rich medium (Moniakis et al., 1999). Conditions that impair CVC function reduce the rate of Ca2+ secretion and antisense-patA RNA or calcineurin antagonists affect cell growth in a high Ca2+ medium (Moniakis et al., 1999). The results suggest a role for CVC in Ca2+ sequestration and excretion pathways, particularly under conditions of high extracellular Ca2+. Consistent with these results, isolated CVs of D.
discoideum have been shown to record Ca2+ (Malchow et al., 2006). It has also been suggested that D. Discoideum`s CVC-P2X receptors are Ca2+ release channels (Ludlow et al., 2009) stimulated by changes in luminal ATP that would be translocated by the ATP-specific transporter into the specific HVAC transporter (Sivaramakrishnan and Fountain, 2012b). A contractile vacuole (CV) is an organelle or subcellular structure involved in osmoregulation and waste disposal. Previously, a CV was known as a pulsed or pulsed vacuole. CVs should not be confused with vacuoles that store food or water. A CV is found mainly in protists and single-celled algae. In freshwater environments, the concentration of solutes inside the cell is higher than outside the cell. Under these conditions, water flows from the environment into the cell by osmosis. Thus, the CV acts as a protective mechanism against cell expansion (and possibly explosion) due to too much water; it expels excess water from the cell by contracting.
However, not all species that have a CV are freshwater organisms; some marine and soil microorganisms also have a CV. Cv is prevalent in species that do not have a cell wall, but there are exceptions. Through the evolutionary process, CV has been largely eliminated in multicellular organisms; However, there are still in the single-celled stage of several multicellular fungi and in different types of cells in sponges, including amoebocytes, pinacocytes and choanocytes. In summary, the contractile vacuole system now appears as an unexpected dynamical system – far beyond its impressive systole/diastole cycle. PtSyb2 and PtSyx2 are SNAREs found exclusively in this complex organelle, in all its parts except the decorated spongioma (where ATPase H+ is exclusively found). There is no evidence of actin in this organelle. Figure 18.8.3D model of the contractile vacuole and the flagellum pocket showing the interconnected spongioma connected to the contractile vacuole (arrows) and concentrated in the anterior region of the contractile vacuole. Some vesicles were also associated with the spongioma (arrowheads). All strains expressing CreMIP1-GFP had a GFP signal at the CV (Fig.
8), indicating that all strains contained MIP1-GFP in the CV membrane. As might be expected from the western blot results, we demonstrated additional GFP fluorescence (most likely in lytic vacuoles and cytoplasm) in UVM4-MIP1GFP-4 and, to a lesser extent, in UVM4-MIP1GFP-3. Video microscopy showed that the large vacuole at the end of the diastole shrinks asymmetrically (collapses towards the particles). In addition, CreMIP1-GFP is never integrated into the PM during systole (see S1 video in additional hardware). Studies with multiple protozoa, especially those that live free, have shown that the contractile vacuole plays a fundamental role in the regulation of osmotic processes. There are few reports of the presence of such a structure in trypanosomes. The structure has been reported to consist of several tubules connected to a central vacuole near the flagellum pocket (Linder and Staehelin 1977). Aquaporin, a protein involved in water transport, has been identified in T. cruzi epimastigotes and localized in acidocalcisomes and contractile vacuoles (Montalvetti et al., 2004). These structures appear to be involved in the process of osmoregulation. The fusion of acidocalcisomes in the contractile vacuole has been shown to take place in a cyclic AMP-mediated process (Review in Rohloff and Docampo, 2008).
The tetrahymene cell usually has a single contractile vacuole (CV, Elliott and Kennedy, 1973) located near the posterior pole of the cell. This osmoregulatory organelle (Rifkin, 1973) accumulates cyclically (diastolene phase) and dissipates accumulated fluid (Systol phase) (Organ et al., 1972; Patterson and Sleigh, 1976) from one to three (2 on average) (Loefer et al., 1966; Nanney, 1966b) kontraktile vacuol pores (CVP). These are visible on the cell surface as circular openings 0.5 to 1 μm wide (Allen and Wolf, 1979), usually slightly positioned at the cytoproct position near the BB series number 5 and 6 (Elliott and Bak, 1964b; Loefer et al., 1966; Nanney, 1966b, 1972; Ng, 1977). The number and position of CVPs correlate with the total number of BB series in the cell (Nanney, 1966b, 1972), specifically with cell geometry, since cells « reduce the relative distance between successive ones. right-post-oral » BB rows (Frankel, 2000a, p. 91; cf. Nanney, 1966b, p. 316). This description explains the positioning of CVs both in normal tetrahymene cells (with a single straight post-oral BB line, line #1) and in cells with duplicate cortical structures (with two OAs and therefore two straight post-oral BB lines).
Weiss et al. (1977a) described groups of visible particles in plasma membrane freezing preparations that superimpose the region of the contractile vacuol. Aggregation of these particles into circular networks both in the plasma membrane and in the underlying membrane of the contractile vacuol appeared to take place at the time of vacuole discharge. .